I love using keyboard shortcuts to get things done faster. Here are the main ones I use in Google Reader.

p/n – navigate up and down through feeds without expanding
k/j – navigate up and down through feeds and expand feeds
N/P – navigate up and down through folders (in the left sidebar)

o – toggle a feed view open or closed
O – toggle a folder
u – toggle left sidebar

a – Add a new feed

? – Show all the shortcuts

All the shortcuts for Google Reader. A Google Experiment makes similar shortcuts work for Google search results.